Method of improving the coefficient of friction between contacting metal surfaces and article produced thereby



2,787,966 BETWEEN April 9, 1957 METHOD OF IMPROVING RAYMOND J l mry s BY V 16.!

A'LT'YS United States Patent METHOD OF IMPROVING THE COEFFICIENT OF FRICTION BETWEEN CONTACTING METAL SURFACES AND ARTICLE PRODUCED THERE- BY Raymond J. Lyons, Palos Heights, 111., assignor to National Aluminate Corporation, Chicago, 111., a corporation of Delaware Application May 2, 1955, Serial No. 505,375

19 Claims. (CI. 104-1) The present invention relates to a new and improved antislip treatment of metal surfaces and more particularly to a method and a composition for increasing the coefficient of friction between the bearing surface of a metal wheel and a metal surface on which it operates. The invention is especially concerned with the provision of chemical means for reducing the wheel slippage between locomotive wheels and rails.

The past several decades have produced railway locomotives possessing great power and weight, thus enabling long, heavily-laden trains to be pulled by single engines. With the advent of the extremely heavy locomotive it was felt that driving wheel slip would be eliminated. It was soon discovered, however, that the increased static weight carried on the driving wheels did not solve the problem to any great extent. Track sanding techniques were developed but this only partially alleviated the condition. Wheel slippage has proven to be an erratic condition which has not in all cases been satisfactorily explained.

In one explanation of the problem, rail slip is said to result from a tough invisible oil film on the wear band of the rail. Traflic and heat destroy this film and high adhesion results. When a light rain occurs or when the rails reach the dew point, as the result of the relatively high humidity, a water vapor film forms across the wear band where it may contact oil deposits on the edge of a rail with the result that a film of oil creeps through and replaces the water film. The oil deposits on the rail sides act as reservoirs for the formation of new oil films and water acts as the transporting agent. The oil deposits on the rail come from journal box oil leakage by way of the outside face and outer portion of the tread of the car wheels. There are other sources of contamination such as road crossings, rail lubricators, and the like.

The importance of solving the problem is strikingly illustrated when it is realized that only of the engines weight can be utilized as tractive force when the rails are greasy and moist, and 30% when the rails are clean, dry and sanded. Even a small improvement in these figures, as expressed in the terms of increased coefficient of friction, would enable railway locomotives to operate more efiiciently and economically as well as providing improved braking for railway locomotives and rolling stock.

It is therefore an object of this invention to provide a method for raising the coefiicient of friction between railway car wheels and rails.

Another object is to raise the coefiicient of friction between railway car wheels and rails having an oil film thereon.

A further object is to provide a method of decreasing slippage between railway wheels and rails.

Another object is to provide a chemical treatment to prevent locomotive slippage on dry, wet, or oily rails.

Still a further object is to enable railroad locomotives to utilize more of their tractive forces on wet oily rails than has heretofore been considered possible.

2,787,966 Patented Apr. 9, 1957 "ice An additional object of the invention is to produce a railway rail containing an adherent coating of a material which substantially prevents slippage between the rail and a locomotive or railway car wheel.

Still a further object of the invention is to provide a rail treating anti-slip composition which is relatively easy to apply and which will remain stable over substantial periods of time.

Another object of the invention is to provide a rail treating anti-slip composition which is stable at temperatures below the freezing point of water.

Still another object of the invention is to provide a new and improved method for treating the contacting surfaces of railway car wheels and/or tracks in order to increase the coefficient of friction therebetween. Other objects will appear hereinafter.

in accordance with the invention is has been found that the coemcient of friction between a metal wheel bearing surface and a metal surface in contact therewith can be increased by applying to at least one of the contacting surfaces a jelly-like to pasty suspension of colloidal silica in a non-lubricating hydrophobic liquid. Only a thin film of the anti-slip composition is required in order to increase the coelficicnt of. friction.

The invention is especially important where exceptionally high pressures are developed at the contacting surfaces as is the case, for example, between railway car wheels and the tracks upon which the railway vehicles operate. in the preferred practice of the invention good results have been obtained by applying to at least one of said contacting surfaces a thin film of a composition consisting essentially of a jelly-like to pasty suspension of at least 5% by weight of a finely divided silica having a surface area of at least 25 square meters per gram with a non-lubricating hydrophobic organic liquid having a viscosity of 26 C. not greater than 35 centipoises.

The finely divided silica employed for the purpose of the invention can be any finely divided silica which is capable of forming a homogeneous, jelly-like to pasty composition with a non-lubricating hydrophobic liquid having a viscosity at 26 C. not greater than 35 centipoises. A silica having a surface area of at least 25 square meters per gram usually has an ultimate particle size not greater than about millimicrons. In general, the diameter of the silica particles will be within the range from about 1 to about 100 millimicrons. While the specific surface area of the silica particles is preferably at least 25 square meters per gram, it usually will not exceed 1000 square meters per gram, and a preferred range of specific surface areas is from about 25 m. g. to about 400 m. g.

A number of different types of silicas can be prepared by well known methods and many of these are available commercially. The following examples are given to illustrate various types of silicas which can be employed for the purpose of the invention:

1. A silica in the form of very small discrete particles having a gel structure within the particles prepared by reacting sodium silicate and an acid at a pH below 3.0 to give a silica sol, polymerizing the silicic acid in the sol sufliciently to make the sol viscous, mixing an organic hydrogen donor bonding agent, such as tertiary butyl alcohol, with the sol, dissolving salt in the mixture whereby a phase separation occurs giving a hydrogen bonder phase containing the silicic acid and an aqueous brine phase, polymerizing the silicic acid further in the bonder phase until hydrated silica is precipitated in the form of discrete particles, separating the precipitated silica from the mother liquor and washing free of salt.

2. A hydrated amorphous silica powder consisting of super colloidal aggregates of ultimate units of from to 50 millimicrons in diameter described in Chemical Engineering 54, 177 (1947), having a specific surface area of about 240 square meters per gram and a bulk density of about 0.064 gram per cc. at 3 pounds per square inch gauge.

3. An amorphous silica aerogel having a specific surface area of about 160 m. /g., as determined by nitrogen adsorption, and a bulk density of about 0.087 gram per cc. at 3 pounds per square inch gauge (Santocel C).

4. An amorphous silica powder consisting of super colloidal aggregates of ultimate units having an average diameter of about millimicrons, a surface area of about 100 m. /g., and containing a small amount of calcium (1% to 2% by weight), known as "Hi-Sil.

5. An amorphous silica powder consisting of super colloidal aggregates having a surface area of about 200 m. /g., sold under the name K-3.

6. A silicate treated with heavy metal salts or hydrous heavy metal oxides to form heavy metal silicates which are water insoluble and usually amorphous as determined by X-ray determination as, for example, a precipitated hydrated calcium silicate having a molar ratio of SiOz/CaO equal to about 3.25, containing aggregates of ultimate particles of the order of to 50 millimicrons in diameter, described in Chemical and Engineering News 24, 3147 (1946), and marketed as Silene EF. This product is a calcium silicate having the following analysis:

CaO percent by weight 19.0 SiOz do 67.0 Loss on ignition do 14.0 pH in water suspension 10.1 Specific gravity 2.10 Bulk density pounds per cubic foot 15-16 Refractive index 1.475

The metal ion in the aforementioned silicas can be an ion other than calcium, as, for example, barium, strontium, magnesium, zinc, cadmium, lead, tin, iron, cobalt and nickel.

7. Colloidal silicas obtained by hydrolysis of silicon tetrachloride.

8. Estersils obtained by the esterification of an amorphous or crystalline silica as described in Iler, U. S. 2,657,149. The estersils employed for the purpose of the invention are preferably obtained by esterifying any of the silicas described under (1) to (7), inclusive, so

as to produce a super colloidal substrate coated with --OR groups, the substrate having a surface of silica and having a specific surface area of from 25 to 900 square meters per gram, there being at least 100 --OR groups per 100 square millimicrons of substrate surface area, and R being a hydrocarbon radical of from 2 to 18 carbon atoms wherein the carbon attached to oxygen is also attached to hydrogen. For the purpose of the present invention, the estersils employed are hydrophobic and usually contain at least 200 ester groups per 100 square millimicrons of substrate surface based on nitrogen adsorption measurements on the unesterified surface.

The invention is not limited to the employment of any particular hydrophobic liquid as the suspending medium for the silica provided that it is non-lubricating. The preferred hydrophobic liquids for the purpose of the invention are aliphatic and aromatic hydrocarbon solvents.

The following tables give specific examples of silicas (Table I), and non-lubricating hydrophobic liquids (Table II) which can be employed in the practice of the invention for the preparation of anti-slip compositions suitable for the purpose of the invention.

TABLE I Surface Ultimate Area, Particle Size, Particle mJ/g. Diameter Size in Milllmlcrons A 0.030 micron..." 30. B 0.0.30 micron. O 0.022 micron. D 150 0.022 micron..." 22. E 40 0.07 micron 22. F 150-200 10-20 milllmicrons. 10-20 G 295-335 8-10mill1miorons. 23-10. H 275-325 8-10 milllmtorons. 8-10. Santoeel O I 110-150 3-5 microns 20-approx. Cab-o-sil c. I -200 0.015-0020 mi- 15-20.

cron. Sylold 244 K 292 1.1-7.0 microns Santocel 54 L 20approx.

TABLE II Solvent Viscosity in cps. at 26 C. No. Name Bronoeo 140 2.0 2.0 1.8 2. 5 2. 2 4. 5 4. 5 6. 5 S. 5 5. 0 3. 0 2. 5 Stoddard Solvent 2.5 Neutral CD Continental 01] 34. 0

In Table I silica A is a calcium silicate containing about 19% CaO and 67% SiOz. Silicas B, C, D, E and F are precipitated silicas. Silicas G and H are incompletely surface esterified silicas of the type described in U. S. 2,657,149. Silica K is a silica derived from a silica gel. Silicas I and L are fine silica aerogels. Silica J is a commercial silica prepared by the hydrolysis of silicon tetrachloride.

Any of the silicas given in Table I can be dispersed in any of the hydrophobic liquids given in Table II. While the hydrophobic liquids are preferably hydrocarbons because such substances are more readily available, it will be understood that liquid chlorinated hydrocarbons, such as liquid chlorinated benzenes, ethylene dichloride, and other substantially inert hydrophobic liquids can be employed which, when mixed with the silica, produce a jelly-like to pasty composition. In general, organic hydrophobic liquids having a viscosity at 26 C. between 2.0 and about 8.5 centipoises have given especially advantageous results.

In the drawing a single figure shows a section of a railway rail containing a thin coating of a composition of the invention applied to the bearing surface thereof.

As shown in the drawing, the rail 1 has a bearing surface 2 to which the coating 3 of the anti-slip composition is applied. The coating of the anti-slip composition may also extend over the surface 4 which comes into contact with the wheel flange of the wheels of locomotives and railway cars.

Evaluation of the invention In order to evaluate the various compositions as agents for improving the coeflicient of friction between railway car wheels and rails, the following test apparatus was employed. A slotted wooden holder comprising two strips of wood was mounted on a bench. The holder was so constructed so as to contain a piece of steel four inches long, one inch wide and one-quarter inch thick, herein referred to as a rail. The steel rail was heat treated and had a tensile strength of 164,200 pounds per square inch, yield point of 159,200 pounds per square inch, a percent elongation of 17.3%, and decarburization to a depth of 0.008 inch. An analysis of this steel showed it to con tain the following:

Percent by weight Carbon .3 1 Manganese .5 8 Phosphorus .016 Sulfur .0 l6

Silicon .29

Chromium 1.000

Molybdenum .222

A U-shaped member made of heavy strap steel was formed having two perpendicular pieces attached to the tips of the U. A diameter hole was bored in the center of the base of the U. A 1%" diameter steel ball having a Brinell hardness of 500 was welded to a threaded steel rod. The threaded steel rod was placed in the hole formed in the U-shaped steel member and fastened with a nut so that the steel ball was within the cradle of the U. The perpendicular arms were fitted with small steel boxes capable of holding lead shot or other weighted material. The U-shaped member was placed on the rail so the steel ball rested on the surface. On either side of the inverted U, wires were attached at a point slightly above the rail surface. Next to the other ends of the wire was a short piece of string attached over a fixed pulley, the top of which was approximately coplanar with the surface of the rail. At the opposite end of the string was a suspended container which could be filled with weights.

In operation, the boxes were filled with lead shot in an amount which, when included with the weight of the cradle and fixtures, were calculated to exert a pressure at point of contact on the rail of 73,900 pounds per square inch. The weight of the U-shaped member and ball was 3,065 grams, which, for the purposes of the experiment may be considered as the operative downward pressure. The suspended container was filled gradually with leadshot until the steel ball just started to slide. This amount of weight is considered as the force necessary to overcome the friction existing between the ball and the rail. By using these two factors, the coeificient of friction may readily be evolved from the following simple equation:

Coefiicient of friction= where P equals 3,065 grams and F equals the weight necessary to move the 3,065 grams.

At the start of each series of tests the rail was cleaned with scouring powder, rinsed with distilled water and dried with cellulose tissues. Periodic inspections were made at the contacting surface and when scratches occurred, the ball and rail were polished with emery paper to renew the surface finish.

To simplify the experimental results the forces necessary to overcome the friction of the steel ball and the rail were recorded in grams. The tests were run by simply smearing a light coating of the composition to be tested over the rail and running the tests while the material was still wet unless otherwise indicated.

In order to establish a working basis for comparing the test results obtained, series of tests were run wherein both the rail and the steel ball were perfectly clean. The average of ten such tests showed a force of 1835 grams necessary to move the ball. When a visible film of journal box oil was applied to the rail the average was 620 grams. All of the tests hereinafter described were conducted with a film of journal box oil at all times initially apparent on the surface of the rail. Hence, readings in excess of 620 indicated compositions of enhanced anti-slip properties. The following examples illustrate the results obtained and indicate the utility of the invention.

EXAMPLE I The following table illustrates the results obtained with silica B dispersed in a concentration of 20% by weight in a variety of non-lubricating hydrocarbon liquids as well as in lubricating oils. All of the oils shown are bydrocarbon in nature. The tests were run using thin coatings smeared over the metal surfaces. The readings in grams are in most instances the average of five consecutive runs.

TABLE III Solvent Viscosity iu cos. at Force in 26 G. Grams No. Name 1 lironoco 140 2.0 2,120 2 Bronoco 75... 2, 0 2.120 3.. Heptane... 1.8 2,100 4 Mineral Spirits 2. 5 2,060 5 'Ioluene H... 2, 2 2,025 6.. Bronoco Base 0 4. 5 2,000 7.. .....\lo 4.5 1,91) ti Mineral Seal ()i 6. 5 1,000 0 Sovncitle 54413.... H. 5 1,930 10"". Sinclair 105 5.0 1310 11 Alpha-Phone" 3. 0 1,400 121 Dipenteuc..... 2.5 1,1 0 13 10 W l\I0tor OIL. .0. 4i. 5 500 14. Heavy Duty 10 W 1 Iotn 4.3. 0 540 15. Stoddard Fol vent 2. 5 l, 400 ML Neutral CD Continental 34, 0 1,320 17 Journal Box 011 344.0 020 From the above Table III it can be seen that compositions 13, 14 and 17 which contained lubricating oils gave poor results. The other compositions containing relatively lower viscosity liquid hydrocarbons gave good results. In all cases jelly-like to pasty compositions were formed at the 20% concentration of silica. In some instances evidence of syneresis was apparent but did not detract from the elfectiveness.

EXAMPLE II An anti-slip composition was prepared from 20% by weight of silica D and by weight of Stoddard Solvent forming a viscous composition. The average force required to move the ball over the steel rail containing a thin film of this composition was 1400 grams.

EXAMPLE III 10% by weight Silica K was added to by weight of mineral seal oil making a light, salve-like composition. The force necessary to move the ball over the rail containing a thin film of this composition averaged 1600 grams.

EXAMPLE IV 20% by weight of Silica B was mixed with 80% by weight of mineral seal oil to produce a salve-like composition. in ten runs the average force required to move the ball over the rail coated with a thin film of this compositicn was 1755 grams.

EXAMPLE V 20% by weight of Silica B was added to 80% by weight of solvent No. 7, Table III. A good homogeneous product was formed. The average force required to move the ball over the rail coated with this product was 1506 grams.

EXAMPLE VI 24% by weight of Silica A was added to 76% by weight of mineral seal oil to form a salve-like product. The average of nine tests showed the force necessary to move the ball over a rail coated with a thin film of this composition to be 2183 grams. Prior to the last three tests the ball was wiped clean with cleansing tissue, yet the high readings persisted.

EXAMPLE VII 15% by weight of Silica F was dispersed in mineral spirits to form a salve-like composition. In five runs the average force required to move the ball over the rail coated with a thin film of this composition was 1780 grams.

EXAMPLE VIII The procedure was the same as that of Example VII except that Silica C was used. The average force required to move the ball over the rail coated with a thin film of the resultant composition was 1900 grams.

EXAMPLE IX 20% by weight of Silica D was dispersed in 80% by weight of tetrachloroethylene. A thin coating of the resultant salve-like composition was applied to the rail. The average force required in three successive runs while the rail was wet with the salve-like composition was 2250 grams.

EXAMPLE X 15% by weight of silica coated with silicon oxyhydride (see U. S. Patent 2,705,206) was dispersed in 85% by weight of solvent No. 1, Table III. A jelly-like paste was formed. The average force in four passes required to move the ball over the rail coated with this composition was 1138 grams.

EXAMPLE XI 20% by weight of a treated silica sold by Linde Air Products Corporation as LM-3 Treated HiSil" (see U. S. Patents 2,705,206 and 2,705,222) was suspended in solvent No. 1, Table III. A jelly-like paste was formed. The average force in four passes required to move the ball over the rail coated with this composition was 1862 grams.

In another series of tests the non-lubricating hydrocarbon liquids of Table III were coated on the oiled rail alone with no substantial improvement in anti-slip properties.

Since the compositions of the present invention are jelly-like to pasty substances it is quite evident that uniformly controlled application of the materials is somewhat difficult to achieve. It has been discovered, however, that merely by applying a thin film, such as would be achieved by rubbing the steel specimen (rail) with the fingers, a good treatment was alforded. This is duplicated in practice on operating railroad locomotives merely by having a swabbing or similar type applicating mechanism to apply the material either to the surfaces of the rail or to the wearband of the wheels of the locomotive.

While the invention is primarily designed to be applied to the contacting surfaces of diesel locomotive wheels and the rails upon which they run, it also has equal effectiveness when it is applied to the wheels of other railway car vehicles such as boxcars, passenger cars, and the like. The invention has also equal application in the application to the contacting surfaces of the wheels and rails of such forms of transportation as streetcars and cars used in the operation of various types of mines.

The quantity of the anti-slip composition of the present invention required to increase the coefficient of fric tion between railway car Wheels and tracks is subject to some variation but will usually be within the range of l to 5 gallons on the track surface per one mile of tworail track.

The term non-lubricating as used herein with reference to the hydrophobic liquids employed to suspend the silica is intended to cover those hydrophobic liquids which have no substantial lubricating effect. It would be possible, of course, for a hydrophobic liquid to have a slight lubricating effect which is more than counteracted by the anti-slip properties of the colloidal silica particles.

The invention is hereby claimed as follows:

l. The method of improving the coefiicient of friction between contacting metal surfaces capable of moving one with respect to the other which comprises applying to at least one of the contacting surfaces a thin coating of a suspension of colloidal silica in a non-lubricating hydrophobic liquid, and bringing said metal surfaces into contact with one another with said colloidal silica therebetween.

2. The method of improving the coefficient of friction between contacting metal surfaces capable of moving one with respect to the other which comprises applying to at least one of the contacting surfaces a thin coating of a suspension of at least 5% by weight of a silica having a specific surface area of at least 25 square meters per gram in a non-lubricating hydrophobic liquid, and bringing said metal surfaces into contact with one another with said colloidal silica therebetween.

3. The method of improving the coefficient of friction between railway cars and tracks which comprises applying to at least one of the contacting surfaces thereof a thin coating of a suspension of at least 5% by weight of a silica having a specific surface area of at least 25 square meters per gram in a non-lubricating hydrophobic liquid.

4. The method of improving the coefficient of friction between railway cars and tracks which comprises applying to at least one of the contacting surfaces thereof a thin coating of a suspension of at least 5% by weight of an amorphous silica having a specific surface area of at least 25 square meters per gram and an ultimate particle size of from 1 to millimicrons in diameter in a nonlubricating organic hydrophobic liquid having a viscosity at 2 C. of not greater than 35 centipoises.

5. The method of improving the coefficient of friction between railway cars and tracks which comprises applying to at least one of the contacting surfaces thereof a thin coating of a suspension of at least 5% by weight of an amorphous silica having a specific surface area of from 25 to 400 square meters per gram and an ultimate particle size of from 1 to 100 millimicrons in diameter in a non-lubricating organic hydrophobic liquid having a viscosity at 26 C. of not greater than 8.5 centipoises.

6. The method of improving the coefficient of friction between railway car wheels and tracks which comprises applying to at least one of the contacting surfaces thereof a coating of a jelly-like to pasty suspension of at least 5% by weight of a hydrophobic silica having a specific surface area of at least 25 square meters per gram and an ultimate particle size of from 1 to 100 millimicrons in a non-lubricating organic hydrophobic liquid, said hydrophobic silica being an esterified silica containing at least 200 OR groups per 100 square millimicrons of substrate surface area wherein R is a hydrocarbon radical of from 2 to 18 carbon atoms and the carbon attached to oxygen is also attached to hydrogen.

7. The method of improving the coefficient of friction between railway car wheels and tracks which comprises applying to at least one of the contacting surfaces thereof a coating of a jelly-like to pasty suspension of a precipitated hydrated silica in the form of discrete particles having a specific surface area of at least 25 square meters per gram and having an average diameter within the range from 1 to 100 millimicrons in a non-lubricating hydrophobic organic liquid having a viscosity at 26 C. of not greater than 8.5 centipoises.

8. The method of improving the coefficient of friction between railway car wheels and tracks which comprises applying to at least one of the contacting surfaces thereof a coating of a jelly-like to pasty suspension of a hydrated amorphous silica powder consisting of supercolloidal aggregates of ultimate units of from 10 to 50 millimicrons in diameter having a specific surface area of at least 25 square meters per gram in a non-lubricating organic hydrophobic liquid having a viscosity at 26 C. of not greater than 8.5 centipoises.

9. The method of improving the coefficient of friction between railway car wheels and tracks which comprises applying to at least one of the contacting surfaces thereof a coating of a jelly-like to pasty suspension of an amorphous silica aerogel having a specific surface area of at least 25 square meters per gram in a non-lubricating organic hydrophobic liquid having a viscosity at 26 C. of not greater than 8.5 centipoises.

10. The method of improving the coefficient of friction between railway car wheels and tracks which comprises applying to at least one of the contacting surfaces thereof coating of a jelly-like to pasty suspension of an amorphous silica powder consisting of supercolloidal aggregates of ultimate units having an average diameter within the range from 1 to 100 millimicrons, specific surface area of at least 25 square meters per gram and containing calcium in chemically combined form.

11. A railway rail having its wheel bearing surface coated with a coating of a colloidal silica dispersed in a non-lubricating hydrophobic liquid.

12. A railway rail having its wheel bearing surface coated with a coating of a hydrophobic colloidal silica.

13. A railway rail having its wheel bearing surface coated with a thin coating of a jelly-like to pasty suspension of at least 5% by weight of an amorphous silica having a specific surface area of at least 25 square meters per gram and an ultimate particle size of from 1 to 100 millimicrons in a non-lubricating hydrophobic liquid having a viscosity at 26 C. of not greater than 35 centipoises.

14. A railway rail having its wheel bearing surface coated with a thin coating of a jelly-like to pasty suspeusion of at least 5% by weight of a hydrophobic silica having a specific surface area of at least 25 square meters per gram and an ultimate particle size of from 1 to 100 millimicrons in a non-lubricating organic hydrophobic liquid, said hydrophobic silica being an esterified silica containing at least 200 -OR groups per 100 square millimicrons of substrate surface area wherein R is a hydrocarbon radical of from 2 to 18 carbon atoms and the carbon attached to oxygen is also attached to hydrogen.

15. A railway rail having its Wheel bearing surface coated with a thin coating of a jelly-like to pasty suspension of a precipitated hydrated silica in the form of discrete particles having a specific surface area of at least 2.5 square meters per gram and having an average diameter within the range from 1 to 100 millimicrons in a non-lubricating hydrophobic organic liquid having a viscosity at 26 C. of not greater than 8.5 centipoises.

16. A railway rail having its wheel bearing surface coated with a thin coating of a jelly-like to pasty suspension of a hydrated amorphous silica powder consisting of supercollcidal aggregates of ultimate units of from 10 to rniilimicrons in diameter having a specific surface area of at least 25 square meters per gram in a nonlubricating organic hydrophobic liquid having a viscosity at 26 C. of not greater than 8.5 centipoises.

17. A railway rail having its wheel bearing surface coated with a thin coating of a jelly-like to pasty suspension of an amorphous silica aerogel having a specific surface area of at least 25 square meters per gram in a non-lubricating organic hydrophobic liquid having a viscosity at 26 C. of not greater than 8.5 centipoises.

18. A railway rail having its wheel bearing surface coated with a thin coating of a jelly-like to pasty suspension of an amorphous silica powder consisting of supercolioidal aggregates of ultimate units having an average diameter within the range from 1 to millimicrons, a specific surface area of at least 25 square meters per gram and containing calcium in chemically combined form.

19. A structure having two metal surfaces capable of motion one with respect to the other and adapted to engage each other by frictional contact, at least one of said surfaces being coated with a thin coating of a colloidal silica dispersed in a non-lubricating hydrophobic liquid.

References Cited in the file of this patent UNlTED STATES PATENTS 1,666,167 Connolly -H Apr. 17, 1928 2,408,656 Kirk Oct. 1, 1946 2,643,048 Wilson June 23, 1953 2,657,149 ller Oct. 27, 1953 

19. A STRUCTURE HAVING TWO METAL SURFACES CAPABLE OF MOTION ONE WITH RESPECT TO THE OTHER AND ADAPTED TO ENGAGE EACH OTHER BY FRICTIONAL CONTACT, AT LEAST ONE OF SAID SURFACES BEING COATED WITH A THIN COATING OF A COLODIAL SILICA DISPERSED IN A NON-LUBRICATING HYDROPHOBIC LIQUID. 